Intracranial atherosclerotic disease (ICAD) is the most common cause of stroke throughout the world. Patients with severe arterial stenosis and a recent stroke or transient ischemic attack are at high risk of recurring stroke. In an attempt to improve the clinical outcome of patients with severe, symptomatic ICAD, percutaneous transluminal angioplasty and stenting have become treatment options over the last years. The SAMMPRIS trial has shown that endovascular treatment does not have favorable outcomes when compared to aggressive medical management. See Chimowitz M, Lynn M, Derdeyn C, et al. Stenting versus aggressive medical therapy for intracranial arterial stenosis. N Engl J Med. 2011;365(11):993-1003. However, patient inclusion of this trial was based on angiographically verified stenosis and did not include a determination of the components of the stenotic plaque, which may be a cause for bias.
Although catheter angiography is currently the gold standard imaging technique for ICAD, it is an invasive procedure that conveys a significant risk of morbidity and mortality. In addition, this technique merely demonstrates vessel narrowing and does not provide characteristics of the atherosclerotic plaque, nor information about the vessel wall or the underlying etiology. With less invasive angiography methods such as MRA and CTA, the degree of stenosis is not always fully appreciated and may not disclose the underlying source. See Feldmann E, Wilterdink J, Kosinski A, et al. The stroke outcomes and neuroimaging of intracranial atherosclerosis (SONIA) trial. Neurology. 2007;68(24):2099-2106.
High resolution vessel wall MRI has shown to be an excellent technique to differentiate between the various pathologies that may be the cause of the stenosis and even allow characterization of plaque composition. See Xu W H, Li M L, Gao S, et al. In vivo high-resolution MR imaging of symptomatic and asymptomatic middle cerebral artery atherosclerotic stenosis. Atherosclerosis. 2010; 212(2):507-511; van der Kolk A G, Zwanenburg J J M, Brundel M, et al. Intracranial vessel wall imaging at 7.0-T MRI. Stroke. 2011; 42(9):2478-2484; Swartz R, Bhuta S, Farb R, et al. Intracranial arterial wall imaging using high-resolution 3-tesla contrast-enhanced MRI. Neurology. 2009; 72(7):627-634; Skarpathiotakis M, Mandell D, Swartz R, Tomlinson G, Mikulis D. Intracranial atherosclerotic plaque enhancement in patients with ischemic stroke. AJNR Am JNeuroradiol. 2012; Qiao Y, Steinman D A, Qin Q, et al. Intracranial arterial wall imaging using three-dimensional high isotropic resolution black blood MRI at 3.0 Tesla. JMRI J Magn Reson Im. 2011; 34(1):22-30; Mandell D M, Matouk C C, Farb R I, et al. Vessel wall MRI to differentiate between reversible cerebral vasoconstriction syndrome and central nervous system vasculitis preliminary results. Stroke. 2012; 43 (3):860-862; and Li M, Xu W, Song L, et al. Atherosclerosis of middle cerebral artery: evaluation with high-resolution MR imaging at 3T. Atherosclerosis. 2009; 204(2):447-452.
Various vessel wall imaging sequences have been proposed to use different techniques to suppress the signal of blood and obtain high resolution image data. However, a standard of reference to quantify their sensitivity and specificity is currently not available. See Degnan A, Gallagher G, Teng Z, Lu J, Liu Q, Gillard J. MR angiography and imaging for the evaluation of middle cerebral artery atherosclerotic disease. AJNR Am JNeuroradiol. 2012; 33(8):1427-1435.
Several different manufacturing processes of vascular replicas have been demonstrated in previous studies. The patient-specific vasculature models were first obtained either by injecting methylmethacrylate into the human cadavers to get vascular lumen casts of the part of interest or sending data derived from images generated from the imaging facilities to 3D printer for rapid prototyping. In the former method, postmortem alterations, including the shrinkage of arterial trees, produced dimensional errors of the in vitro model. Different methods including repeated painting, dip-spin processing, and lost-wax technique were then applied to the casts to form the elastomeric replicas. The repeated panting and dip-spin procedure was time-consuming and not reproducible. On the other hand, the major concern of lost-wax technique was the fragility of the wax, which resulted in the breakage of the vessel branches smaller than 1 mm.
References to the prior art include Ikeda S, Arai F, Fukuda T, et al. An in vitro patient-tailored model of human cerebral artery for simulating endovascular intervention. Med Image Comput Comput Assist Intery Int Conf Med Image Comput Comput Assist Intery 2005; 8:925-32; Suzuki Y, Fujitsuka M, Chaloupka J C. Simulation of endovascular neurointervention using silicone models: imaging and manipulation. Neurol Med Chir (Tokyo) 2005; 45:567-72, discussion 572-73; Gruber A, Bavinszki G, Killer M, et al. In vitro training model for endovascular embolization of cerebral aneurysms. Minim Invasive Neurosurg 1997; 40:121-23; Barath K, Cassot F, Rufenacht D A, et al. Anatomically shaped internal carotid artery aneurysm in vitro model for flow analysis to evaluate stent effect. AJNR Am J Neuroradiol 2004; 25:1750-59; Cortez M A, Quintana R, Wicker R B. Multi-step dip-spin coating manufacturing system for silicone cardiovascular membrane fabrication with prescribed compliance. Int J Adv Manuf Technol 2006;34:667-79; Gailloud P, Pray J R, Muster M, et al. An in vitro anatomic model of the human cerebral arteries with saccular arterial aneurysms. Surg Radiol Anat 1997; 19:119-21; Knox K, Kerber C W, Singel S A, et al. Rapid prototyping to create vascular replicas from CT scan data: making tools to teach, rehearse, and choose treatment strategies. Catheter Cardiovasc Intery 2005; 65:47-53; Markl M, Schumacher R, Kuffer J, et al. Rapid vessel prototyping: vascular modeling using 3T magnetic resonance angiography and rapid prototyping technology. MAGMA 2005; 18:288-92; Seong J, Sadasivan C, Onizuka M, et al. Morphology of elastase-induced cerebral aneurysm model in rabbit and rapid prototyping of elastomeric transparent replicas. Biorheology 2005;42:345-61; Sugiu K, Martin J B, Jean B, et al. Artificial cerebral aneurysm model for med medical testing, training, and research. Neurol Med Chir (Tokyo) 2003; 43:69-72, discussion 73; Wetzel S G, Ohta M, Handa A, et al. From patient to model: stereolithographic modeling of the cerebral vasculature based on rotational angiography. AJNR Am J Neuroradiol 2005; 26:1425-27; and Ohta M, Handa A, Iwata H, et al. Poly-vinyl alcohol hydrogel vascular models for in vitro aneurysm simulations: the key to low friction surfaces. Technol Health Care 2004; 12:225-33.
Silicone elastomer is frequently used for preparation of vascular replicas. However, silicone elastomer has a high friction coefficient and is tacky which can make advance of endovascular devices difficult. To date, polyvinyl alcohol (PVA) is used as an alternative material to construct vascular replicas in the application of neurovascular modeling. The high water content of PVA hydrogel not only gives vascular replicas a naturally lubricated surface but also provides good visibility.
There is a need for improved methods of imaging or modeling vascular systems so that more effective treatment may be provided to patients.